Concentric line construction



Oct. 31, 1950 R. A. HERRING, JR 2,527,549

CONCENTRIC LINE CONSTRUCTION Filed Feb 4, 194:5

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Patented Oct. 31, 1950 CON CENTRIC LINE CONSTRUCTION Robert A. Herring, Jr., Washington, D. 0.

Application February 4, 1943, Serial No. 474,663

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 4 Claims.

This invention relates to concentric transmission line construction, and is particularly directed to improvements in concentric line sections which may be employed as resonant circuits. The invention is further applicable to resonant concentric tanks useful as protective elements and decoupling elements in duplex transmission and reception with a single antenna. Devices of this nature are known in the prior art and conventionally include a voltage operated switching device for shifting the impedance of the elements in duplex operation.

It is an object of the invention to provide a concentric transmission line construction Wherein adjustable circuit elements within the transmission line may be adjusted from outside the transmission line.

A second object of the invention is to provide a concentric transmission line construction including an interrupted central conductor with adjustable circuit elements connected between its separate portions.

A further object of the invention is to provide for the adjustment of internal circuit elements of a transmission line section through an aperture extending from the outside of the section along a bore in the central conductor, and into the space within the section.

Another object of the invention is to provide for tuning and otherwise adjusting a resonant transmission line section by adjustable circuit elements within the section, and to effect the adjustments from outside the section by means which do not disturb the symmetry of the fields therein.

A more specific object of the invention is to provide for adjusting circuit elements within a transmission line section by means of an operating member contained in a bore in the central conductor.

In d-uplexing systems, especially for pulse transmission and echo reception, it is the practice to couple the receiver to the transmission line through a transformer which effects automatic decoupling durin transmission periods. This is accomplished by the use of a resonant tank including a switching element for detuning the tank on the application of high voltage from the transmitter. Similar tank elements may be employed for decoupling the transmitter from the receiver during reception. I

In installations of this type it is necessary to tune such a, resonant tank to the exact fre quency employed by an adjustable capacitor within the section. It is also desirable to adjust the switching element for optimum periormance in relation to the transmitting voltage. Means for adjusting these circuit elements from outside the tank are [provided by this invention, which will be further understood with reference to the exemplary embodiment shown in the drawing where:

Fig. 1 is an elevational view, partly in section, of a concentric line section embodying the invention;

Fig. 2 is a schematic representation of a duplexing system employing the invention in a protective tank, and

Fig. 3 is a schematic representation Ofa duplexing system employing the invention in a protective tank and in a transmitter decoupling tank.

As shown in Fig. 1, the tank comprises a cylindrical outer conductor or shell I, conducting end plates 2 and 3 fixed in the ends of the outer conductor, and an interrupted central conductor having spaced portions 4 and 5. The inner and outer conductors are thus short circuited by the end plates at their outer extremities. The central conductor portions are positioned in holes provided in end plates 2 and 3, and are supported intermediate their lengths by spacing members 6 and l, which comprise diametrically extending bars of insulating material peripherally shaped to engage the inner face of the outer conductor. The spacin members are apertured to receive the central conductor portions, and are fixed by screws 8 passing through the outer conductor.

Connection of concentric lines to the tank section may be made by conventional connector taps 9 and I0. Connector tap 9 may be jointed to a main transmission line by an intervening section and connector Ill may be connected to a concentric line of a, smaller diameter.

The spaced central conductor portions are connected by a capacity directly across the gap between them, and for this purpose opposed con denser elements II and [2 are mounted on central conductor portions 4 and 5 respectively.

The condenser elements, which may be circularly formed conducting plates, are preferably adjustably mounted for tuning the section. As shown, element I2 is integrally attached to collar I3 slidable along the central conductor portion 5, on which it may be permanently positioned by set screw l4.

Condenser element I l is movably mounted relative to element l2, so that the tank may be tuned by adjusting the capacity across the central conductor portions. It is important that the tuning capacity be directly across the gap in half-wave series gap tanks, since parallel capacity will render the tank difficult of correct adjustment in the field, due to possibility of undesired resonances close to the operating frequency, which almost completely destroy the protective function of the tank. Through the construction disclosed, the parallel capacity is minimized, and further, by mounting the adjustable element for movement longitudinally of the section and parallel to the outer conductor, the capacity between the element and the outer conductor remains substantially unchanged on tuning.

The desired longitudinal adjustment of element is effected by movement of its supporting member l5, which is slidably mounted within a bore in central conductor portion 4. Member I5 is internally threaded and is actuated by engagement of rotatable shaft l8, externally threaded as shown at H. Shaft I8 is mounted also within the bore in central conductor portion 4, and is reduced in its outer portion to form extension 2|] which projects beyond end plate 2 and carries tuning knob 22. At the inner end of extension is provided shoulder 2|, which abuts against a positioning bushing 26 pressed into the end of the bore in central conductor portion 4. Knob 22 is fixed on extension 20 beyond the outer face of end plate 2 by set screw 23. Friction spring 24 apertured to receive extension 20, is contained in slot 25 in the base of tuning knob 22 and simultaneously holds shoulder 2| against collar 23 and prevents accidental rotation of knob 22 and shaft l8.

On rotation of shaft 28, member |5 is axially adjusted through their threaded engagement, l5 being prevented from rotating by pin it slidably engaged in slot IT in central conductor portion 4. Consequently the tuning of the section is easily effected by manual operation of knob 22.

The spaced central conductor portions 4 and 5 are also connected by a discharge device consisting of opposed spark electrodes 21 and 28. The electrodes are adjust/ably mounted to permit variation of the discharge gap independently of the tuning of the section. Electrode 28 is mounted on shaft 30 longitudinally movable in a bore in central conductor portion 5. Opposing electrode 27 is mounted in a longitudinally fixed position, being carried by shaft l8.

Adjustment of the gap spacing is obtained by rotation of shaft 30 which is threaded through bushing 3| fixed in the inner end of central conductor portion 5. passes through a centering collar 32 in the outer end of central conductor portion 5, and extends beyond the outer face of end plate 3. The end of shaft 30 is slotted for screw driver adjustment, as shown at 35. When proper gap spacing is obtained, shaft 30 may be locked by a nut 34 threaded onto portion 33 of the shaft.

It will be understood that suitable sealing elements may be interposed between nut 34 and end plate 3, and between shoulder 2| and collar 26, if the tank is to be employed in a concentric line system containing pressure. It should also be pointed out that whereas the invention has been shown as embodying a discharge switching element positioned medially of the length of the section in accordance with the teaching of appli cation, Serial No. 452,534 of Varela and Herring, filed July 27, 1942, such is not a necessary feature of this invention.

Operation of resonant sections embodying the The outer end of shaft 30 invention may be explained with reference to the duplexing systems shown schematically in Figs. 2 and. 3.

In Fig. 2, is a transmitter connected to an antenna (not shown) by untuned concentric line 4|. At point 42 a quarter wave section 43 is tapped into line 4|. Point 42 is selected as having a high impedance looking into the main transmission line 4| toward the transmitter during receiving conditions.

Quarter wave section 43 is tapped into the duplexing resonant tank 44 at point 45. Tank 44 is constructed as shown in Fig. 1, and includes capacitor 46 and discharge gap 4'! controlled respectively by tuning knob 48 and shaft 49. Receiver transmission line 50 is tapped into duplexing tank at point 5|.

In the system shown the duplexing tank comprises a half wave section in which the tap points 45 and 5| are symmetrically placed to match lines 43 and 50, whose characteristic impedances are identical. The tank is tuned to resonance by knob 48 for the selected operating frequency. Consequently the impedances facing each other are correctly matched and the receiver is properly coupled to the main transmission line with the resonant tank acting as a transformer. The transmitter branch presents high impedance at point 42 and permits efficient reception.

Under transmitting conditions high potentials are present in the duplexing tank. By means of shaft 49, gap 41 is adjusted to ionize under these conditions, which effectively shunts capacitor 48 by a low resistance. This throws the tank off resonance, and the impedance measured between point 45 and ground is the equivalent of a, low resistance and a somewhat higher inductive reactance in series. The length of quarter wave section 43 is adjusted to give anti-resonance with the impedance presented at point 45 so that a high pure resistance is seen at point 42 looking into line 43. Consequently very little power is drawn from the main transmission line under transmitting conditions. Furthermore, the voltage appearing across the main line is stepped down by the transformer action of the quarter wave line 43, and is again reduced by the reactive impedance of the tank itself. Through this means the voltage applied to the receiver is limited to a safe level.

Due to the fact that the impedance at point 42 of the main transmission line looking toward the transmitter may vary with transmitter adjustment, it is desirable to control this impedance directly. A duplexing system incorporating the invention for accomplishing this result is shown in Fig. 3.

Transmitter 52 is connected to an antenna (not shown) by untuned transmission line 53. A receiver protective tank 54 is coupled into the main line at point 55 by quarter wave section 56. Preferably but not necessarily the protective tank is of the type disclosed in Fig. 1, in which case the operation of this part of the system is in all rer spects similar to that described in connection with Fig. 2.

In order to decouple the transmitter from the transmission line system for reception, a decoupling tank 51 is connected into the main line by a quarter wave section 58 at a point 59 an odd number of quarter waves from point 55.

Decoupling tank 51 is'a half wave series gap section similar to the one disclosed in Fig. 1, with the exception that tap I0 is eliminated. The tank and its associated line 58 are tuned to resonance on the operating frequency, as above described. In receiving conditions the decoupling tank resonates and presents a pure resistance at point 99, much higher than the characteristic impedance of lines 53, 59 and 58. Hence, at point 59 a low resistance is shunted across the'main line, which therefore presents a high impedance at point 55 looking toward the transmitter. Consequently during reception the transmitter is effectively decoupled.

For transmitting, the gap in decoupling section 5! is adjusted to ionize under the conditions then present, whereupon a high pure resistance is presented at point 59 looking into quarter wave section 58. This operation is exactly as described above in connection with the operation of receiver protective tank 94 in Fig. 2 and presents an inconsequential load to the transmitter.

It is therefore apparent that the half-wave series gap tank may be employed as a protective tank or as a decoupling tank, as well as serving both functions in a system as illustrated in Fig. 3.

Although I have shown and described certain and specific embodiments of this invention I am fully aware of the many modifications possible thereof. This invention is not to be restricted except insofar as is necessitated by prior art and by the spirit of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. In a concentric transmission line section having a metal conductor short circuiting each.

of its ends, and including a hollow central conductor containing a bore and having an interrupted portion, said bore and interrupted portion constituting aperture means communicating with the interior of the section, adjustable discharge means and adjustable capacitor means connected across the interrupted portion, and actuating means operatively connected with the adjustable means movably mounted in the aperture means.

tor means connecting said spaced portions, andv movable actuating members operatively connected with the adjustable means mounted within the hollow central conductor, each central conductor portion receiving one of said members.

3. In a concentric transmission line section having a metal conductor short circuiting each of its ends, and including an interrupted hollow central conductor comprising two spaced portions, two movable members mounted within the hollow central conductor, each central conductor portion receiving one of said members, adjustable discharge means connecting the central consaid spaced portions, a second bore extending from the outside of said section through another of said spaced portions, a plurality of circuit elements within said section operatively coupled therewith and actuating means for said circuit elements movably mounted in said first and said second bores.

ROBERT A. HERRING, J R.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,035,958 Girardeau Aug. 20, 1912 1,304,868 Franklin May 27, 1919 2,030,180 Potter Feb. 11, 1936 2,088,722 Potter Aug. 3, 1937 2,135,353 .Rorden Nov. 1, 1938 2,143,671 Zottu Jan. 10, 1939 2,337,219 Zottu M Dec. 21, 1943 2,410,641 Evans Nov. 5, 1946 2,415,962 Okress Feb. 18, 1947 FOREIGN PATENTS Number Country Date 183,699 Great Britain Aug. 3, 1922 

